The present invention relates to the field of testing equipment for electro-optical systems such as laser rangefinder/designators, and more particularly to an improved test system which employs holographic optical elements.
A laser rangefinder is an equipment which can send out laser pulses and detect the returning pulses reflected from the target; the delay time of the pulses determines the target range. The equipment also contains a sight unit for the operator to aim at the selected target.
A laser designator is an equipment similar to the laser rangefinder, except that its purpose is to illuminate the selected target. The scattered laser energy is used to guide "smart" bombs or artillery for converging into the target.
The laser designator and the laser rangefinder are sometimes combined into one piece of equipment.
For a laser rangefinder or designator to be useful, its laser output must meet certain energy level and beam divergence requirements. The alignment between the sight unit and the laser pointing must be properly maintained. And, the subsystem for measuring the delay of return signals must function correctly. It is thus necessary to test the equipment periodically for its output, alignment and ranging accuracy.
Presently, the laser beam quality can be tested with, for example, an automatic laser test set (ALTS) marketed by Hughes Aircraft Company. The ALTS equipment uses diode matrix array to record the laser beam intensity profile. The analysis of this profile will give the information on beam energy, divergence and pointing. When coupled with a visual reticle by the use of a beamsplitter, the ALTS can also be used to test beam alignment. The ranging accuracy can be tested with, for example, a simulated optical range target (SORT), also developed by Hughes Aircraft Company. The SORT equipment includes focusing optics and an optical fiber delay line. The laser energy is focused into one end of the fiber and reflected back from the other end. The laser energy re-emits from the first end with proper delay time and attenuation to simulate the return signal. The return signal then travels back to the rangefinder for ranging test.
Conventional lenses, beamsplitters and mirrors can be used to combine the ALTS and the SORT equipment with the visual reticle into a compact package to test the rangefinder for its beam quality, alignment and ranging accuracy. However, the disadvantages of this approach include the following: (1) traditional mirrors, lenses, and beamsplitters are bulky and heavy; and (2) mechanical design and assembly processes are complicated by the relatively large number of optical elements involved.